Base64Encode编码函数

char* Base64Encode(const char *str,int length)
{
     static   char   base64_table[] =
     { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
        'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
        'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/', '/0' };

     static char  base64_pad = '=';
     const char *current = ( const char*)str;
     int i = 0;
     char *result = ( char *)malloc(((length + 3 - length % 3) * 4 / 3 + 1) * sizeof(char));
     while (length > 2)
    {
          /* keep   going until we   have   less   than   24   bits */
          result[i++] = base64_table[current[0] >> 2];
          result[i++] = base64_table[((current[0] & 0x03) << 4) + (current[1] >> 4)];
          result[i++] = base64_table[((current[1] & 0x0f) << 2) + (current[2] >> 6)];
          result[i++] = base64_table[current[2] & 0x3f];
          current += 3;
          length -= 3; /* we   just   handle   3   octets   of   data */
      }
     /* now deal   with   the   tail end of   things */
     if (length != 0)
     {
          result[i++] = base64_table[current[0] >> 2];
          if (length > 1)
          {
               result[i++] = base64_table[((current[0] & 0x03 ) << 4) + (current[1] >> 4)];
               result[i++] = base64_table[(current[1] & 0x0f) << 2];
               result[i++] = base64_pad;
          }
          else
          {
               result[i++] = base64_table[(current[0] & 0x03) << 4];
               result[i++] = base64_pad;
               result[i++] = base64_pad;
          }
     }
     result[i] = '/0'; // printf("%s/n",result);
     return result;
}